Guides and examples: email providers, i18n, monorepos, MJML and Beefree, upgrading to 0.3

[ivoIturrieta]

Stacked on the MJML and Beefree importers PR (#70), which is stacked on the 0.3.0 library PR (#69): it shows only the guides and examples. Merge it after both, with its base changed to main first. The repo's tests only run on pull requests into main, so CI starts here once the base is main; until then, the validation below was run locally.

What

• Email providers: the content-workflows example sends with 14 providers. Mailgun, Azure, MailerSend, Scaleway, Plunk, Lettermint, Brevo, Inbound and EUSend are added, each tested against mocked endpoints. Guide: email providers.
• i18n example: one template in English and Arabic with react-intl, react-i18next and next-intl, including right-to-left output. It runs in CI. Guide: translations and right-to-left, written for 0.3 (inline <FormattedMessage>/<Trans> children, right alignment by default in RTL).
• Migrating from MJML: leads with npx @unlayer/migrate <dir> --from mjml: what becomes editable blocks, what stays MJML's HTML, includes, MJML 3, what the check compares against. The hand mapping stays, for tuning the output.
• Migrating from Beefree (new): the JSON it reads, the HTML export to put beside it so the template is checked, ? for unverified, and the declared differences.
• Upgrading: what changes from 0.2 to 0.3 and what to check (13 items: the text block's markup, images sized in their slot, the editor's base stylesheet, the Provider, right-to-left alignment, migrate's range, …), the new entries, and the 0.1 to 0.2 guide.
• Monorepos: one Elements copy, React resolution and workspaces, previewing with a small render script.
• No unpublished packages: the guides don't mention the local preview package or the CLI commands that need it.
• READMEs: point to the Elements skill in unlayer/unlayer-skills, and list @unlayer/migrate as published, with its MJML and Beefree sources. The changelog points to the upgrade guide (its 0.1.1 to 0.2.1 history is in @unlayer/react-elements 0.3.0: Tailwind, Markdown, code, fonts, async, codegen and editor-parity fixes #69).

Validation

• content-workflows: typecheck and 13/13 tests pass. i18n: typecheck and 4/4 pass.
• The MJML and Beefree guides were checked by running the CLI on the committed fixtures (MJML 19 ✓; Beefree 10 ✓ and 7 ?; --strict, includes outside the folder, MJML 3, unknown Beefree versions and the Elements version check).
• Each upgrade item was checked by rendering with 0.2.1 and with 0.3.0.
• Every relative link in the changed docs resolves. A trial merge onto @unlayer/react-elements 0.3.0: Tailwind, Markdown, code, fonts, async, codegen and editor-parity fixes #69's latest changelog is clean.